bmptopnm reads a Microsoft Windows or OS/2 BMP file as
input. and pro- duces a PBM, PGM, or PNM image as output. If
the input is colormapped and contains only black and white,
the output is PBM. If the input is colormapped and contains
only black white and gray, the output is PGM. Otherwise, the
output is PPM.

bmptopnm understands BMP files compressed with run
length encoding (RLE4/RLE8), but not if that encoding
includes a delta (which is rare). bmptopnm recognizes the
delta and issues an error message.

Before Netpbm 10.18 (September 2003), this program could
not convert BMP images with the BI_BITFIELDS format
("compression type"). It would recognize the
format and issue an error message.

bmptopnm cannot convert OS/2 BMP files with 16 bits per
pixel (only because the author did not have a complete
specification for them). It recognizes the format and issues
an error message. Before Netpbm 10.16 (June 2003), it also
could not convert Windows BMP files with 16 bits per
pixel.